So, what is it like cycling up Palomar Mountain from Hwy 76 and S6 - South Grade Road?
Endless... At least that's what if feels like. The climb isn't steep (it averages only 7.5%), but it is very consistent and very long. From start to finish the slope varies more than 2% at only one 150 yds long stretch, about 5 miles into the 11.5 miles long climb. That false flat on Hwy 76 just before the South Grade Rd turn off is the only break you'll get in the entire climb. Once you make the turn onto South Grade Rd, it's 6.5-8% grade the rest of the way.
Hwy 76 has a bit of shoulder to ride up, but it is pretty narrow and collects a bit of debris. There is almost always some traffic, and it is always high speed (and tends to be trucks, SUV's or trailers). Once you turn onto South Grade Rd (S6), traffic becomes light to non-existence and there is good shoulder to ride on the rest of the way.
It takes me about 110 minutes to climb Palomar from the south side, and
only about 22 minutes to descend it (and that's because I'm a careful
rider and slow considerably down once I get back onto Hwy 76 and its car
traffic). If you haven't cycled up Palomar from the south before, you
should... but try to make it on a weekday as South Grade Rd is way too
popular a motorcycle road on weekends that it is quite unsafe.
If you are going up it during the warm months (June-Nov), take at least two big bottles of water (at least one bottle should really be water, since you'll be plagued to the edge of sanity by nasty flies whose sole ambition in life is to get at all the salt around your eyes deposited there by your sweat... And nothing like a good rinse of water would persuade the flies to leave your eyes alone for more than a few seconds).
Oak Knolls Campground at the base of South Grade Rd has a store where you can get water, cold drinks and some candy bars. There is no other water stop along the route (the artesian springs at mile 11 is all dried up). Once you top out, though, there is Mother's Kitchen to lunch at, a nice restroom with running water, and Palomar Mountain General Store with cold drinks and candies.